This invention relates to an electronic musical instrument capable of sounding a tone signal generated in digital after converting it to an analog signal and, more particularly, to an instrument capable of converting digital tone signals of different tone groups individually to analog signals.
Tone signals generated by an electronic musical instrument can be classified into groups on the basis of some common standard such, for example, as the keyboard type, tone color and tone effect. Such groups of tones are herein called tone groups. In an electronic musical instrument, tone generation routes are generally provided individually for different types of tone groups. In an electronic musical instrument of a digital tone generation system, therefore, a digital tone generation circuit (or channel) is provided for each of a plurality of tone groups classified according to a classification item which is suitably chosen from the standpoint of design of the instrument, a digital tone signal being generated with respect to each of these tone groups. For example, in a prior art electronic musical instrument, these tone groups are suitably called such as "orchestra tones", "special tones", "preset tones" and "custom tones" according to difference in the tone forming system and switches for selecting a tone color, tone level and tone effect are provided for each of these tone groups. Since a digital tone signal must be generated individually for each of these tone groups, a problem arises as to how a digital-to-analog conversion circuit should be provided. For converting a digital tone signal to an analog signal while maintaining sufficient resolution and dynamic range, an expensive multi-bit type digital-to-analog converter is required. It is undesirable in view of the cost and scale of circuit to employ many of such digital-to-analog converter. Nevertheless, digital-to-analog conversion in the electronic musical instrument comprising a plurality of tone groups has been performed individually for each of the tone groups and an analog tone signal has had to be produced separately for each necessary tone group. One requirement therefor is to increase a tonal effect by distributing analog tone signals for respective tone groups among various speakers such as left, right and center ones. Another requirement is to enable a different tone level adjustment separately for each of the tone groups. Still another requirement is to impart a modulation effect to a specific tone group in a state of an analog tone state. For these reasons, a plurality of digital-to-analog converters had to be used, one being provided for each of these tone groups, in spite of the cost and the large scale circuit design it involves.
It is an object of the present invention to provide an electronic musical instrument capable of effecting the digital-to-analog conversion efficiently and at a low cost by employing only a small number of digital-to-analog converters.